[PATCH 3/6] selftests: forwarding: lib: add run_cmd_grep helper for feature probing

In some forwarding tests, it is necessary to check for features or
specific keywords in command output before proceeding.

Introduce the run_cmd_grep helper in lib.sh. This helper executes a
command and searches for a specific pattern in its output.

Signed-off-by: Aleksei Oladko <redacted>
---
 tools/testing/selftests/net/forwarding/lib.sh | 19 +++++++++++++++++++
 1 file changed, 19 insertions(+)

diff --git a/tools/testing/selftests/net/forwarding/lib.sh b/tools/testing/selftests/net/forwarding/lib.sh
index 0a474b02371d..dcf17c19ad77 100644
--- a/tools/testing/selftests/net/forwarding/lib.sh
+++ b/tools/testing/selftests/net/forwarding/lib.sh

@@ -2163,3 +2163,22 @@ has_unicast_flt()
 
 	[[ $promisc == 1 ]] && echo "no" || echo "yes"
 }
+
+run_cmd_grep_common()
+{
+	local find="$1"; shift
+	local cmd="$*"
+
+	if [ "$VERBOSE" = "1" ]; then
+		echo "COMMAND: ${cmd} 2>&1 | grep -q '${find}'"
+	fi
+	$cmd 2>&1 | grep -q "${find}"
+	return $?
+}
+
+run_cmd_grep() {
+	run_cmd_grep_common "$@"
+	rc=$?
+	check_err $rc
+	return $rc
+}

-- 
2.43.0